Endovascular support device and Method

ABSTRACT

An endovascular support device for treatment of chronic restenosis or other vascular narrowing is disclosed together with a method of manufacture and a method for delivering a plurality of such devices to an affected area of a vessel. In a preferred embodiment, the endovascular support device comprises a unitary wire-like structure configured to form a plurality of upper and lower peaks which may be compressed for delivery to an affected area of a coronary or peripheral vessel in a human, and then expanded to maintain a passageway through the vessel.

FIELD OF THE INVENTION

[0001] The present invention relates generally to medical devices, andparticularly relates to implantable devices for treating narrowing ofcoronary or peripheral vessels in humans.

BACKGROUND OF THE INVENTION

[0002] Cardiovascular disease, including atherosclerosis, is the leadingcause of death in the U.S. The medical community has developed a numberof methods for treating coronary heart disease, some of which arespecifically designed to treat the complications resulting fromatherosclerosis and other forms of coronary arterial narrowing.

[0003] The most impelling development in the past decade for treatingatherosclerosis and other forms of coronary narrowing is percutaneoustransluminal coronary angioplasty, hereinafter referred to simply as“angioplasty” or “PTCA”. The objective in angioplasty is to enlarge thelumen of the affected coronary artery by radial hydraulic expansion. Theprocedure is accomplished by inflating a balloon within the narrowedlumen of the coronary artery. Radial expansion of the coronary arteryoccurs in several different dimensions and is related to the nature ofthe plaque. Soft, fatty plaque deposits are flattened by the balloon andhardened deposits are cracked and split to enlarge the lumen. The wallof the artery itself is also stretched when the balloon is inflated.

[0004] PTCA is performed as follows: A thin-walled, hollow guidingcatheter is typically introduced into the body via a relatively largevessel, such as the femoral artery in the groin area or the brachialartery in the arm. Access to the femoral artery is achieved byintroducing a large bore needle directly into the femoral artery, aprocedure known as the Seldinger Technique. Once access to the femoralartery is achieved, a short hollow sheath is inserted to maintain apassageway during PTCA The flexible guiding catheter, which is typicallypolymer coated, and lined with Teflon, is inserted through the sheathinto the femoral artery. The guiding catheter is advanced through thefemoral artery into the iliac artery and into the ascending aorta.Further advancement of the flexible catheter involves the negotiation ofan approximately 180 degree turn through the aortic arch to allow theguiding catheter to descend into the aortic cusp where entry may begained to either the left or the right coronary artery, as desired.

[0005] After the guiding catheter is advanced to the ostium of thecoronary artery to be treated by PTCA, a flexible guidewire is insertedinto the guiding catheter through a balloon and advanced to the area tobe treated. The guidewire provides the necessary steerability for lesionpassage. The guidewire is advanced across the lesion, or “wires” thelesion, in preparation for the advancement of a polyethylene, polyvinylchloride, polyolefin, or other suitable substance balloon catheteracross the guide wire. The balloon, or dilatation, catheter is placedinto position by sliding it along the guide wire. The use of therelatively rigid guide wire is necessary to advance the catheter throughthe narrowed lumen of the artery and to direct the balloon, which istypically quite flexible, across the lesion. Radiopaque markers in theballoon segment of the catheter facilitate positioning across thelesion. The balloon catheter is then inflated with contrast material topermit fluoroscopic viewing during treatment The balloon is alternatelyinflated and deflated until the lumen of the artery Is satisfactorilyenlarged.

[0006] Unfortunately, while the affected artery can be enlarged, in someinstances the vessel restenoses chronically, or closes down acutely,negating the positive effect of the angioplasty procedure. In the past,such restenosis has frequently necessitated repeat PTCA or open heartsurgery. While such restenosis does not occur in the majority of cases,it occurs frequently enough that such complications comprise asignificant percentage of the overall failures of the PTCA procedure,for example, twenty-five to thirty-five percent of such failures.

[0007] To lessen the risk of restenosis, various devices have beenproposed for mechanically keeping the affected vessel open aftercompletion of the angioplasty procedure. Such mechanical endoprostheticdevices, which are generally referred to as stents, are typicallyinserted into the vessel, positioned across the lesion, and thenexpanded to keep the passageway clear. Effectively, the stent overcomesthe natural tendency of the vessel walls of some patients to close backdown, thereby maintaining a more normal flow of blood through thatvessel than would be possible if the stent were not in place.

[0008] Various types of stents have been proposed, although to date nonehas proven satisfactory. One proposed stent involves a tube of stainlesswire braid. During insertion, the tube is positioned along a deliverydevice, such as a catheter, in extended form, making the tube diameteras small as possible. When the stent is positioned across the lesion, itis expanded, causing the length of the tube to contract and the diameterto expand. Depending on the materials used in construction of the stent,the tube maintains the new shape either through mechanical force orotherwise. For example, one such stent is a self-expanding stainlesssteel wire braid. Other forms of stents include various types tubularmetallic cylinders expanded by balloon dilatation. One such device isreferred to as the Palmaz stent, discussed further below.

[0009] Another form of stent is a heat expandable device. This device,originally designed using NITINOL by Dotter has recently been modifiedto a new tin-coated, heat expandable coil by Regan. The stent isdelivered to the affected area on a catheter capable of receiving heatedfluids. Once properly positioned, heated saline is passed through theportion of the catheter on which the stent is located, causing the stentto expand. Numerous difficulties have been encountered with this device,including difficulty in obtaining reliable expansion, and difficultiesin maintaining the stent in its expanded state.

[0010] Perhaps the most popular stent presently under investigation inthe United States is referred to as the Palmaz stent. The Palmaz stentinvolves what may be thought of as a stainless steel cylinder having anumber of slits in its circumference, resulting in a mesh when expanded.The stainless steel cylinder is delivered to the affected area by meansof a balloon catheter, and is then expanded to the proper size byinflating the balloon.

[0011] Significant difficulties have been encountered with all prior artstents. Each has its percentage of thrombosis, restenosis and tissuein-growth, as well as varying degrees of difficulty in deployment.Another difficulty with at least some of prior art stents is that theydo not readily conform to the vessel shape. In addition, the relativelylong length of such prior art stents has made it difficult to treatcurved vessels, and has also effectively prevented successfulimplantation of multiple such stents. Anticoagulants have historicallybeen required at least for the first three months after placement. Theseand other complications have resulted in a low level of acceptance forsuch stents within the medical community, and to date stents have notbeen accepted as a practical method for treating chronic restenosis.

[0012] Thus there has been a long felt need for a stent which iseffective to maintain a vessel open, without resulting in significantthrombosis, which may be easily delivered to the affected area, easilyexpanded to the desired size, easily conformed to the affected vessel,and easily used in multiples to treat curved vessels and varying lengthsof lesions.

SUMMARY OF THE INVENTION

[0013] The present invention substantially reduces the complications andovercomes the limitations of the prior art devices. The endovascularsupport device of the present invention comprises a device having verylow mass which is capable of being delivered to the affected area bymeans of a slightly modified conventional balloon catheter similar tothat used in a standard balloon angioplasty procedure.

[0014] The support device of the present invention may then be expandedby normal expansion of the balloon catheter used to deliver the stent tothe affected area, and its size can be adjusted within a relativelybroad range in accordance with the diagnosis of the treating physician.

[0015] Because of the range of diameters through which the supportdevice of the present invention may be expanded, it may be customexpanded to the specific lesion diameter, and is readily conformable tothe vessel shape. In addition, a plurality of support devices of thepresent invention may be readily implanted in a number commensurate withthe length of the lesion under treatment. As a result, curved or “S”shaped vessels may be treated.

[0016] The stent, or endovascular support device, of the presentinvention may preferably be comprised of implantable quality high gradestainless steel, machined specially for intravascular applications. Thesupport device may comprise, in effect, a metal circle or ellipsoidformed to create a plurality of axial bends, thereby permittingcompression of the stent onto a delivery catheter, and subsequentexpansion once in place at the affected area.

[0017] It is one object of the present invention to provide a stentwhich substantially overcomes the limitations of the prior art.

[0018] It is a further object of the present invention to provide astent capable of being implanted simply and reliably.

[0019] Another object of the present invention is to provide a stentwhich does not result in significant thrombosis at the point of implant.

[0020] Yet another object of the present invention is to provide a stentwhich can be selectively sized in accordance with the anatomicconfiguration dictated by the lesion itself.

[0021] A still further object of the present invention is to provide amethod for supplying an endovascular support device which permits aplurality of such devices to be implanted commensurate with the lengthof the lesion under treatment.

[0022] These and other objects of the present invention can be betterappreciated from the following detailed description of the invention,taken in conjunction with the attached drawings.

FIGURES

[0023]FIG. 1 shows a perspective view of an endovascular support deviceconstructed according to the present invention, in its expanded form.

[0024]FIG. 2 shows a support device constructed according to the presentinvention and compressed onto a balloon catheter.

[0025]FIG. 3 shows a support device compressed onto a balloon catheteras shown in FIG. 2 and positioned within a sectioned portion of anaffected area of a artery or other vessel.

[0026]FIG. 4 shows a support device according to the present inventionin its expanded form within a sectioned portion of a vessel including alesion.

[0027]FIG. 5 shows a support device of the present invention in itsexpanded form within a sectioned portion of a lesion after removal ofthe balloon catheter.

[0028]FIGS. 6a-b show alternative configurations of a support deviceaccording to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0029] Referring first to FIG. 1, an endovascular support device 10,referred to hereinafter more conveniently as a stent, constructed inaccordance with the present invention can be seen in perspective view.The stent 10 of FIG. 1 is shown in its expanded form, prior tocompression over a suitable delivery system as discussed in detailhereinafter.

[0030] In a preferred embodiment, the stent 10 comprises a single pieceof material, bent to form a plurality of upper axial turns 12 and loweraxial turns 14, In the embodiment shown in FIG. 1, four upper turns 12are connected to the four lower turns 14 by substantially straightsegments 16. The axial turns 12 and 14 can be seen to permit the stent10 to be compressed or expanded over a wide range while stillmaintaining significant mechanical force, such as required to prevent avessel from restenosing. While a preferred embodiment comprises a singlepiece of material, in some instances a suitably welded wire may beacceptable.

[0031] It will be appreciated that the number of turns 12 and 14 canvary over a reasonably wide range, and may in fact vary between two andten such turns or peaks. However, it is currently believed that theoptimum number of turns or peaks will range between three and five formost applications, and particularly for cardiovascular applications.

[0032] The stent 10 is preferably constructed of implantable materialshaving good mechanical strength. An embodiment which has provensuccessful in preliminary testing is machined from 316LSS implantablequality stainless steel bar stock. The bar stock is machined to formsubstantially a toroid, which is then acid etched in phosphoric andsulfuric acid at approximately 180° to 185° to break the edges. Theetched toroid is then plated with copper to avoid galling and to providelubricity.

[0033] The copper plated toroid is then bent to the shape of the stent10 shown in FIG. 1, after which the copper plating is stripped from thestent. The stent is then returned to the acid bath to reduce the wiresize to the desired diameter, which is in the range of 0.002″ to 0.025″.It is presently believed that the optimum wire size for the finalproduct is in the range of 0.008″ to 0.009″. It will be appreciated thatthe strength of the stent—that is, its ability to prevent restenosis—isinversely proportional to the number of peaks or turns in the stent, sothat stents having a greater number of turns will typically be formed oflarger wire diameters. Finally, although not required in all cases, theoutside of the stent may be selectively plated with platinum to provideimproved visibility during fluoroscopy. The cross-sectional shape of thefinished stent may be circular, ellipsoidal, rectangular, hexagonal,square, or other polygon, although at present it is believed thatcircular or ellipsoidal may be preferable.

[0034] The minimum length of the stent, or the distance between theupper turns 12 and lower turns 14, is determined in large measure by thesize of the vessel into which the stent will be implanted. The stent 10will preferably be of sufficient length as to maintain its axialorientation within the vessel without shifting under the hydraulics ofblood flow (or other fluid flow in different types of vessels), whilealso being long enough to extend across at least a significant portionof the affected area. At the same time, the stent should be short enoughas to not introduce unnecessarily large amounts of material as mightcause undue thrombosis. Typical cardiovascular vessels into which thestent 10 might be implanted range from 1.5 millimeters to fivemillimeters in diameter, and corresponding stents may range from onemillimeter to two centimeters in length. However, in most instances thestent will range in length between 3.5 millimeters and 6 millimeters.Preliminary testing of stents having a length between 3.5 millimetersand 4.5 millimeters has been performed with good success outside theUnited States, and testing on animals is also ongoing.

[0035] Once the wire size of the stent 10 has been reduced to thedesired size, the stent 10 may be crimped onto a balloon 100, as shownin FIG. 2, for delivery to the affected region 102 of a vessel 104 suchas a coronary artery. For the sake of simplicity, the multiple layers ofthe vessel wall 104 are shown as a single layer, although it will beunderstood by those skilled in the art that the lesion typically is aplaque deposit within the intima of the vessel 104.

[0036] One suitable balloon for delivery of the stent 10 is manufacturedby Advanced Cardiovascular Systems, Inc., of Santa Clara, Calif.(“ACS”), and is eight millimeters in length with Microglide* on theshaft only. The stent-carrying balloon 100 is then advanced to theaffected area and across the lesion 102 in a conventional manner, suchas by use of a guide wire and a guide catheter (not shown). A suitableguide wire is the 0.014″ Hi Torque Floppy manufactured by ACS, and asuitable guiding catheter is the ET.076 lumen guide catheter, alsomanufactured by ACS.

[0037] Once the balloon 100 is in place across the lesion 102, as shownin FIG. 3, the balloon 100 may be inflated, again substantially in aconventional manner. In selecting a balloon, it is helpful to ensurethat the balloon will provide radially uniform inflation so that thestent 10 will expand equally along each of the peaks. The inflation ofthe balloon 100, shown in FIG. 4, causes the expansion of the stent 10from its crimped configuration back to a shape substantially like thatshown in FIG. 1. The amount of inflation, and commensurate amount ofexpansion of the stent 10, may be varied as dictated by the lesionitself, making the stent of the present invention particularly flexiblein the treatment of chronic restenosis.

[0038] Because of the inflation of the balloon, the lesion 102 in thevessel 104 is expanded, and causes the arterial wall of the vessel 104to bulge radially, as simplistically depicted in FIG. 4. At the sametime, the plaque deposited within the intima of the vessel is displacedand thinned, and the stent 10 is embedded in the plaque or otherfibrotic material adhering to the intima of the vessel 104.

[0039] Following inflation of the balloon 100 and expansion of the stent10 within the vessel 104, the boon is deflated and removed. The exteriorwall of the vessel 104 returns to its original shape through elasticrecoil. The stent 10, however, remains in its expanded form within thevessel, and prevents further restenosis of the vessel. The stentmaintains an open passageway through the vessel, as shown in FIG. 4, solong as the tendency toward restenosis is not greater than themechanical strength of the stent 10. Because of the low mass of thesupport device 10 of the present invention, thrombosis is less likely tooccur. Ideally, the displacement of the plaque deposits and theimplantation of the stent 10 will result in a smooth inside diameter ofthe vessel 104, although this ideal cannot be achieved in all cases.

[0040] One of the advantages of the stent 10 is that multiple stents maybe used in the treatment of a single lesion. Thus, for example, in theevent the affected area shown in FIGS. 3 and 4 was longer than the stent10, additional stents 10 could be positioned elsewhere along the lesionto prevent restenosis. In preliminary testing, up to four stents havebeen used successfully along a single lesion. Due to the conformabilityof the stent 10, not only can varying lesion lengths be treated, butcurved vessels and “S” shaped vessels may also be treated by the presentinvention. In instances where it is known in advance that multiplestents will be the preferred method of treatment, a plurality of suchstents may be positioned along a single balloon catheter forsimultaneous delivery to the affected area.

[0041] As discussed above, the number of peaks or turns 12 and 14 in thestent 10 may vary between two and ten. To this end, shown in FIGS. 6aand 6 b are two alternative configurations of the stent 10. Thealternative embodiment shown in 6 a can be seen to have three upper andthree lower peaks or turns, while the embodiment shown in FIG. 6b can beseen to have ten upper and ten lower peaks.

[0042] While the primary application for the stent 10 is presentlybelieved to be treatment of cardiovascular disease such asatherosclerosis or other forms of coronary narrowing, the stent 10 ofthe present invention may also be used for treatment of narrowed vesselsin the kidney, leg, cartoid, or elsewhere in the body. In such othervessels the size of the stent may need to be adjusted to compensate forthe differing sizes of the vessel to be treated, bearing in mind thesizing guidelines provided above.

[0043] Having fully described a preferred embodiment of the invention,those skilled in the art will immediately appreciate, given theteachings herein, that numerous alternatives and equivalents exist whichdo not depart from the present invention. It is therefore to beunderstood that the present invention is not to be limited by theforegoing description, but only by the appended claims.

I claim:
 1. An endovascular support device suitable for implantationwithin a coronary or other vessel within the human body comprising a-unitary member of wire-like material configured to provide a pluralityof upper and lower peaks, the unitary member being capable of beingcompressed for delivery to an affected area of a vessel and thenexpanded to maintain the affected area of a vessel at a diameter largerthan if the support device were not implanted.
 2. A method of treatingnarrowing of coronary or peripheral vessels within humans comprising thesteps of providing a compressible and expandable endovascular supportdevice, compressing the endovascular support device onto a ballooncatheter, advancing the balloon catheter and endovascular support deviceto an affected area, inflating the balloon catheter to expand theendovascular support device within the affected area to thereby preventstenosis of at least a portion of the narrowed length of the vessel, andrepeating the advancing and inflating steps until a sufficient pluralityof endovascular support devices have been expanded within the affectedarea to prevent stenosis along the narrowed length of the vessel.
 3. Amethod of manufacturing an endovascular support device comprisingforming a toroid from a first material, plating the toroid with a secondmaterial having higher lubricity than the first material, bending thetoroid to form a plurality of upper and lower peaks, stripping off thesecond material from the toroid, and reducing the diameter of the benttoroid to a desired size.